Firion -> Frinel
Gus -> Guy

Kain -> Cain
Rydia -> Lydia
Tellah -> Tella
Edward -> Gil
FuSoYa -> Fusuya

Bartz -> Butz

TERRA -> Tina
SABIN -> Mash
CYAN -> Cayene

Aeris -> Aerith

And sometimes, just for fun:

Dagger -> Sarah